LLE Review 136

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Highlights

This volume of the LLE Review, covering July–September 2013, features “Demonstration of the Improved Rocket Efficiency in Direct-Drive Implosions by Using Different Ablator Materials,” which reports on the first experimental study of rocket efficiency where different ablators were used to vary the ratio of the atomic number over the atomic mass. Success of direct-drive implosions critically depends on the ability to create high ablation pressures (~100 MBar) and accelerating the imploding shell to ignition-relevant velocities (>3.7 – 10⁷ cm/s) by using direct laser illumination. It is demonstrated that the implosion velocity of Be shells is increased by 20% compared to C and CH shells in direct-drive implosions. These measurements are consistent with the predicted increase in the hydrodynamic efficiency of 18% for Be and 7% for C compared to a CH ablator.

Additional highlights of research presented in this issue include the following:

• The Bragg angle, rocking curve, and reflection efficiency of a quartz-crystal x-ray imager (Miller indices 234) were measured at photon energy of 15.6909 keV, corresponding to the K_α2 line of Zr using the X15A beamline at the National Synchrotron Light Source at Brookhaven National Laboratory. Using one of the curved crystals, the Zr K_α2 emission was imaged from a hot Zr plasma generated by LLE’s 10-J, Multi-Terawatt laser. Estimates of the reflectivity obtained by comparing the spatially integrated signal from the images to the direct x-ray emissivity of the source were, within experimental error, in agreement with values obtained at the X15A beamline.
• A process for producing ultra-broadband coatings with high reflectivity, high-laser-damage thresholds, and controlled dispersion is demonstrated over 10-in.-aperture substrates. Large-aperture deposition of high-laser-damage-threshold, low-dispersion optical coatings for 15-fs pulses has been developed using plasma-ion–assisted electron-beam evaporation.
• The results of study of the optical signals generated by multiple sinusoidal temporal phase modulations (multi-FM) of a monochromatic field are reported. Analysis and simulation of frequency-modulation-to-amplitude-modulation conversion of arbitrary multi-FM signals are of theoretical and practical importance for high-energy laser systems, where optical pulses are phase modulated in the front end to smooth out the on-target beam profile and prevent potentially catastrophic damage to optical components.
• R. D. Petrasso’s (Plasma Science and Fusion Center, MIT) report on the Fifth Omega Laser Users Group Workshop is presented.
• This volume concludes with a summary of LLE’s Summer High School Research Program, the FY13 Laser Facility Report, and the National Laser Users’ Facility and External Users’ Programs.